Nickel, cobalt and rare earth metals are known as valuable metals and used for various applications in industry. Nickel and cobalt is used for positive electrode materials for secondary batteries and the like. Rare earth metals are used for fluorescent materials, negative electrode materials for nickel-hydrogen batteries, additives for magnets installed in motors, abrasives for glass substrates used for liquid crystal display panels and hard disk drives, and the like.
In recent years, energy savings have been strongly promoted, and in the automobile industry conventional gasoline-engined cars are being rapidly replaced by hybrid cars and electric cars equipped with secondary, batteries using nickel, cobalt and rare earth metals. In lighting equipment, conventional fluorescent lamps are being rapidly replaced by efficient three band fluorescent lamps using rare earth metals such as lanthan, cerium, yttrium, terbium and europium. The above cobalt, nickel and rare earth metals are scarce resources, and most of them depend on imports.
Yttrium and europium have been used for fluorescent substances in cathode ray tube television sets in analog broadcasting; however, in recent years, large numbers of cathode ray tubes have been put out of use because of the transition to liquid crystal television sets. Products which have rapidly spread, such as secondary batteries and three band fluorescent lamps, can be also easily expected to cause a large amount of waste in the future as used products. Thus, nickel, cobalt and rare earth metals, scarce resources, are treated as waste without recycling of the used products, which is not preferred in terms of resource savings and resource security. Nowadays, the establishment of a method for effectively retrieving valuable metals such as nickel, cobalt and rare earth metals from such used products is strongly demanded.
Incidentally, the above secondary batteries include nickel-hydrogen batteries, lithium-ion batteries and the like, and manganese is used, along with the rare metals nickel and cobalt, as the material for their positive electrode materials. The ratio of inexpensive manganese tends to be increased in the place of expensive cobalt in positive electrode materials for lithium-ion batteries. There have been attempts to retrieve valuable metals from used batteries recently, and as one of these retrieval methods, there is a dry method for retrieving metals in which used batteries are thrown into a furnace and dissolved to separate the metals and slag. In this method, however, manganese moves to the slag and thus only nickel and cobalt are retrieved.
Furthermore, a wet method is also known in which used batteries are dissolved in an acid and the metals are retrieved using a separation method, such as a precipitation method, a solvent extraction method or an electrowinning method. As an example of the precipitation method, a method is known in which the pH of a solution containing nickel, cobalt and manganese is adjusted and a sulfidizing agent is added to obtain sulfide precipitates of nickel and cobalt, and a method is also known in which oxide precipitates of manganese are obtained by adding an oxidizing agent (see Patent Document 1). In this method, however, there are problems in that, for example, coprecipitation occurs, and it is difficult to completely separate nickel, cobalt and manganese.
In addition, when nickel is retrieved as a metal by the electrowinning method, it is known that manganese oxides are precipitated on positive electrode surfaces in a system in which a high concentration of manganese exists and positive electrode deterioration is accelerated. Specific fine colored manganese oxides are floated in electrolyte solutions, which causes, for example, clogging of the filter cloth used it electrowinning as well as contamination of nickel metal due to manganese oxides. Therefore, stable operations are difficult to ensure.
In addition, when nickel is retrieved using the solvent extraction method, an acidic extraction agent is widely used. As described above, however, because a large amount of manganese has been used recently for the positive electrode materials in lithium ion batteries, a high concentration of manganese exists in the electrolyte solutions in the batteries. In the present situation, there is no effective extraction agent to selectively and effectively extract nickel, from such a system.
In addition to the recycling of used batteries, in nickel refining which is carried out at present to produce nickel, cobalt also coexists in the nickel, oxide ores used as a raw material and a large amount of manganese also exists in these ores. Therefore, when nickel is refined, there is a great problem of separating it from cobalt and manganese,    Patent Document 1: Japanese Unexamined Parent Application, Publication. No. 2000-234130    Non Patent Document 1: K. Shimojo, H. Naganawa, J. Noro, F. Kubota and M. Goto; Extraction behavior and separation of lanthanides with a diglycol amic acid derivative and a nitrogen-donor ligand; Anal. Sci., 23, 1427-30, 2007 December.